This invention is directed to radiography. In particular, it is directed to a method of imaging a specific radiographic silver halide film or imaging assembly that are useful for providing medical diagnostic images of soft tissues such as in mammography. This method can be carried out to advantage using high peak voltage.
The use of radiation-sensitive silver halide emulsions for medical diagnostic imaging can be traced to Roentgen""s discovery of X-radiation by the inadvertent exposure of a silver halide film. Eastman Kodak Company then introduced its first product specifically that was intended to be exposed by X-radiation in 1913.
In conventional medical diagnostic imaging the object is to obtain an image of a patient""s internal anatomy with as little X-radiation exposure as possible. The fastest imaging speeds are realized by mounting a dual-coated radiographic element between a pair of fluorescent intensifying screens for imagewise exposure. About 5% or less of the exposing X-radiation passing through the patient is adsorbed directly by the latent image forming silver halide emulsion layers within the dual-coated radiographic element. Most of the X-radiation that participates in image formation is absorbed by phosphor particles within the fluorescent screens. This stimulates light emission that is more readily absorbed by the silver halide emulsion layers of the radiographic element.
Examples of radiographic element constructions for medical diagnostic purposes are provided by U.S. Pat. No. 4,425,425 (Abbott et al.) and U.S. Pat. No. 4,425,426 (Abbott et al.), U.S. Pat. No. 4,414,310 (Dickerson), U.S. Pat. No. 4,803,150 (Kelly et al.), U.S. Pat. No. 4,900,652 (Kelly et al.), U.S. Pat. No. 5,252,442 (Tsaur et al.), and Research Disclosure, Vol. 184, August 1979, Item 18431.
While the necessity of limiting patient exposure to high levels of X-radiation was quickly appreciated, the question of patient exposure to even low levels of X-radiation emerged gradually. The separate development of soft tissue radiography, which requires much lower levels of X-radiation, can be illustrated by mammography. The first intensifying screen-film combination (imaging assembly) for mammography was introduced to the public in the early 1970""s. Mammography film generally contains a single silver halide emulsion layer and is exposed by a single intensifying screen, usually interposed between the film and the source of X-radiation. Mammography utilizes low energy X-radiation, that is radiation that is predominantly of an energy level less than 40 keV.
U.S. Pat. No. 6,033,840 (Dickerson) and U.S. Pat. No. 6,037,112 (Dickerson) describe asymmetric imaging elements and processing methods for imaging soft tissue.
Problem to be Solved
In mammography, as in many forms of soft tissue radiography, pathological features that are to be identified are often quite small and not much different in density than surrounding healthy tissue. Thus, the use of films with relatively high average contrast (in the range of from 2.5 to 3.5) over a density range of from 0.25 to 2.0 is typical. Limiting the amount of X-radiation requires higher absorption of the X-radiation by the intensifying screen and lower X-radiation exposure of the film. This can contribute to loss of image sharpness and contrast. Thus mammography is a very difficult task in medical radiography.
Radiographic imaging of soft tissue as in mammography is usually carried out using low peak voltage (kVp), for example 28 kVp, from the imaging equipment to maximize image sharpness. However, the consequence of low peak voltage is higher patient dose.
There remains a need in mammography for a way to minimize patient exposure to radiation while providing optimal radiographic image quality such as image contrast.
The present invention provides an advance in the art with a method of imaging for mammography comprising exposing a patient to X-radiation at a peak voltage greater than 28 kVp using an X-radiation generating device, and providing a black-and-white image of the exposed patient using an imaging assembly comprising:
A) a radiographic silver halide film that comprises a support having first and second major surfaces and that is capable of transmitting X-radiation,
the radiographic silver halide film having disposed on the first major support surface, one or more hydrophilic colloid layers including at least one cubic grain silver halide emulsion layer, and having disposed on the second major support surface, one or more hydrophilic colloid layers including at least one tabular grain silver halide emulsion layer,
wherein the film can be exposed to provide a black-and-white image having a d(xcex3)/d(log E) value greater than 5, and
B) a fluorescent intensifying screen that comprises an inorganic phosphor capable of absorbing X-rays and emitting electromagnetic radiation having a wavelength greater than 300 nm.
In some embodiments, this invention provides a method of imaging for mammography comprising exposing a patient to X-radiation at a peak voltage greater than 28 kVp using an X-radiation generating device, and providing a black-and-white image of the exposed patient using an imaging assembly comprising:
A) a radiographic silver halide film that has a photographic speed of at least 100 and comprises a support having first and second major surfaces and that is capable of transmitting X-radiation,
the radiographic silver halide film having disposed on the first major support surface, one or more hydrophilic colloid layers including at least one cubic grain silver halide emulsion layer, and having disposed on the second major support surface, one or more hydrophilic colloid layers including at least one tabular grain silver halide emulsion layer,
wherein the cubic grain silver halide emulsion layer comprises:
1) a combination of first and second spectral sensitizing dyes that provides a combined maximum J-aggregate absorption on the cubic silver halide grains of from about 540 to about 560 nm, and
wherein the first spectral sensitizing dye is an anionic benzimidazole-benzoxazole carbocyanine, the second spectral sensitizing dye is an anionic oxycarbocyanine, and the first and second spectral sensitizing dyes are present in a molar ratio of from about 0.25:1 to about 4:1,
2) a mixture of a first hydrophilic binder that is gelatin or a gelatin derivative and a second hydrophilic binder other than gelatin or a gelatin derivative, wherein the weight ratio of the first hydrophilic binder to the second hydrophilic binder is from about 2:1 to about 5:1, and the level of hardener in the cubic grain silver halide emulsion layer is from about 0.4 to about 1.5 weight % based on the total weight of the first hydrophilic binder in the cubic grain silver halide emulsion layer,
3) cubic silver halide grains comprising from about 1 to about 20 mol % chloride and from about 0.25 to about 1.5 mol % iodide, both based on total silver in the cubic grain emulsion layer, which cubic silver halide grains have an average ECD of from about 0.65 to about 0.8 xcexcm, and
4) cubic silver halide grains that are doped with a hexacoordination complex compound within part or all of 95% of the innermost volume from the center of the cubic silver halide grains, and
B) a fluorescent intensifying screen that comprises an inorganic phosphor capable of absorbing X-rays and emitting electromagnetic radiation having a wavelength greater than 300 nm.
In preferred embodiments, the present invention provides a method of imaging for mammography comprising exposing a patient to X-radiation at a peak voltage greater than 28 kVp using an X-radiation generating device, and providing a black-and-white image of the exposed patient using an imaging assembly comprising:
A) a radiographic silver halide film having a photographic speed of at least 100 and comprising a transparent film support having first and second major surfaces and that is capable of transmitting X-radiation,
the radiographic silver halide film having disposed on the first major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer, and having disposed on the second major support surface, one or more hydrophilic colloid layers including at least one tabular grain silver halide emulsion layer,
the film also comprising a protective overcoat layer disposed on both sides of the support,
wherein the cubic grain silver halide emulsion layer comprises:
1) a combination of first and second spectral sensitizing dyes that provides a combined maximum J-aggregate absorption of from about 545 to about 555 nm when the dyes are absorbed on the surface of the cubic silver halide grains,
wherein the first spectral sensitizing dye is the following Dye A-2, and wherein the second spectral sensitizing dye is following Dye B-1, the first and second spectral sensitizing dyes being present in a molar ratio of from about 0.5:1 to about 1.5:1, and the total spectral sensitizing dyes in the film is from about 0.25 to about 0.75 mg/mole of silver, 
2) a mixture of a first hydrophilic binder that is gelatin or a gelatin derivative and a second hydrophilic binder that is a dextran or polyacrylamide, wherein the weight ratio of the first hydrophilic binder to the second hydrophilic binder is from about 2.5:1 to about 3.5:1 and the level of hardener in the cubic grain silver halide emulsion is from about 0.5 to about 1.5 weight % based on the total weight of the first hydrophilic binder in the cubic grain silver halide emulsion layer,
3) cubic silver halide grains comprising from about 10 to about 20 mol % chloride and from about 0.5 to about 1 mol % iodide, both based on total silver in the cubic grain silver halide emulsion layer, which cubic silver halide grains have an average ECD of from about 0.72 to about 0.76 xcexcm, and
4) cubic silver halide grains that are doped with a hexacoordination complex compound within 75 to 80% of the innermost volume from the center of the cubic silver halide grains, wherein the hexacoordination complex compound is represented by the following Structure I:
[ML6]n
wherein M is Fe+2, Ru+2, Os+2, Co+3, Rh+3, Ir+3, Pd+3, or Pt+4, L represents six coordination complex ligands that can be the same or different provided that at least three of the ligands are cyanide ions, and n is xe2x88x922, xe2x88x923, or xe2x88x924, and
B) a single fluorescent intensifying screen that comprises an inorganic phosphor capable of absorbing X-rays and emitting electromagnetic radiation having a wavelength greater than 300 nm, the inorganic phosphor being coated in admixture with a polymeric binder in a phosphor layer disposed on a flexible support and having a protective overcoat disposed over the phosphor layer.
The methods of the present invention can further comprise processing the radiographic silver halide film, sequentially, with a black-and-white developing composition and a fixing composition, the processing being carried out within 90 seconds, dry-to-dry.
The present invention provides a means for providing radiographic images for mammography unexpectedly exhibiting improved image quality while minimizing radiation dosage to which patients are exposed. In particular, image quality can be improved with the present invention by increasing image contrast, decreasing xe2x80x9cnoisexe2x80x9d (for example, film granularity), or both. These advantages are possible with a unique radiographic film and imaging assembly and using higher peak voltage (kVp) than normal. Thus, the imaging method of the present invention is carried out at a peak voltage greater than 28 kVp using imaging equipment whereby patient dosage is reduced without sacrificing image quality such as image contrast.
It has been found that the radiographic silver halide films useful in the practice of the present invention can provide image that exhibit desired contrast in the mid-scale region. This contrast can be evaluated by calculating the derivative (or slope) of a gamma vs. log E curve to obtain a term xe2x80x9cd(xcex3)/d(log E)xe2x80x9d that is defined in more detail below. In the practice of the present invention, the films can exhibit a d(xcex3)/d(log E) greater than 5 and preferably greater than 5.5.
In addition, all other desirable sensitometric properties are maintained and the radiographic film can be rapidly processed in the same conventional processing equipment and compositions.